AIDS Vaccine shows promise in monkey experiments

Published: Thursday, March 08, 2001

PAUL RECERAP Science Writer

WASHINGTON {AP} In a study giving new evidence that AIDS can be controlled by vaccine, inoculated monkeys stayed healthy despite exposure to high levels of virus, researchers say. The new vaccine is being fast-tracked toward human testing.

In a report appearing Friday in the journal Science, researchers said the vaccine uses a one-two-three punch, with two shots to prime the immune system to resist the AIDS virus, and a final shot with a modified pox virus to boost protection.

The first two shots use a vaccine containing DNA for three proteins like those found in the AIDS virus. These proteins create a memory that prompts the immune system to attack when the proteins are later detected, said Harriet L. Robinson, senior author of the study.

The booster shot uses a modified smallpox vaccine with the three HIV proteins added. This intensifies the immune system's response against the AIDS virus proteins, she said.

"Our results show that we can protect monkeys against an HIV-like virus using an immunization scheme that is practical for use in people," she said. Robinson noted, however, that the vaccine has not been tested for use in people already infected with HIV.

Dr. Anthony S. Fauci, head of the National Institute of Allergy and Infectious Diseases, said the study "provides some of the best evidence to date that a preventive HIV vaccine may protect against AIDS."

"Although the vaccine did not prevent infection, it continues to keep the virus at nearly undetectable levels for at least several months," he said. "We do not know yet if this vaccine will work in humans, but plans for the necessary clinical studies are under way."

Robinson said the first human trials are expected in less than a year.

The procedure being used gives "a much more effective immunization than with the pox virus alone or by the DNA alone," said Robinson, a professor at the Emory University Vaccine Center and the Yerkes Regional Primate Research Center. "The DNA vaccine has the ability to prompt a very focused response."

In the study, 24 monkeys were inoculated with varying doses of the new vaccine. Four other monkeys received only placebo. Seven months later, all the monkeys were exposed to lethal doses of a virus that mimics HIV, the virus that causes AIDS in humans.

The HIV-mimic virus is used because monkeys cannot be lethally infected by HIV itself. The mimic is constructed from both HIV and SIV, a virus that causes AIDS in monkeys, and is widely accepted as a simian model for HIV.

All four of the control monkeys developed AIDS and were dead within 28 weeks. All the vaccinated monkeys became infected with the virus, but their immune systems, prompted by the vaccine, were able to control the virus and the animals did not become sick.

Robinson said one vaccinated monkey, which received a low dose of the vaccine, has an elevated level of virus and could become sicker. But all the rest "are very, very well," she said.

Dr. Bernard Moss of the NIAID, a co-author and developer the pox virus part of the vaccine system, said that the researchers waited seven months after the monkeys were vaccinated before exposing the animals to the AIDS virus.

"A real vaccine has to provide long-term protection," he said. In earlier vaccine studies, the animals were often exposed to virus within weeks of their shots.

Also, said Moss, the monkeys were exposed to virus loads hundreds of times higher than the typical human exposure to HIV. This proves that the vaccine has a very powerful effect.

Additionally, the monkeys were exposed to the virus rectally. Moss said this more closely resembles the way that the AIDS virus is typically spread among humans. HIV is a sexually transmitted disease.

The two-step booster vaccine "is among the most exciting concepts that we've seen in" monkey testing, Dr. Peggy Johnston, head of the AIDS vaccine program at the National Institutes of Health, said in Science.

The new vaccine resembles one developed at Harvard that also tested successfully. The Harvard vaccine technique required six inoculations and used more of the HIV proteins. Robinson said her vaccine requires only three shots and uses only three proteins.

"Ours is a simpler vaccine," said Robinson, "but the fact that both our studies have achieved this type of control is really encouraging and shows that this will work against the AIDS virus."

Another HIV vaccine made with DNA and a booster using the smallpox vaccine has been developed in England. Tests on humans started this week, with part of the vaccine being tested in England and part in Kenya.

More than a dozen other types of HIV vaccines are currently being studied in programs sponsored by various governments, universities and pharmaceutical companies, but Robinson said her vaccine has the best results in monkey experiments.

"We are ahead with our results in monkeys, but we will need to be fast-tracked to catch up with some of the others" in human trials, Robinson said.